UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 255 
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Contribution from the Bureau of Entomology 
L. O. HOWARD, Chief 
> Sy ? f 
/: SF oe 7 By JOSEF BRUNNER, 
A, . ° . 
9 4 Ponte mological Assistant, Forest Insect Investigations. 
2, NATURE AND CAUSE OF DAMAGE. 
itch seams, gum check, windshake, or whatever these defects may 
be termhéd locally, have ever been recognized as a serious depreciating 
factor in the utilization of Douglas fir (Pseudotsuga taxifolia). 
These defects have heretofore been variously charged to windshake 
(mechanical strain), lightning, frost, blazes, fires, and various other 
unavoidable causes, but investigation of the trouble and its causes 
makes it evident that the work of the larve of the Douglas fir pitch 
moth (Sesia novaroensis Hy. Edw.) is the primary cause of a large 
percentage of these defects. 
DISTRIBUTION AND EXTENT OF DAMAGE. 
In the northern Rocky Mountain and Pacific coast regions it has 
been definitely determined that the Douglas fir pitch moth is re- 
sponsible for at least 90 per cent of this damage. 
A very similar larva,? found working in Douglas fir in the south- 
ern Rocky Mountain district, makes it quite certain that the same 
species is responsible for what similar depreciation in timber value 
may be existing there. 
The loss occasioned by the work of this class of insects causes the 
difference in price between absolutely clear lumber and the lower 
grades or “ dimension stuff.” These insects work in the portion of the 
trunk which later clears itself of branches; hence only logs are 
affected which, were it not for previous infestation by them, would 
yield only the better grades of lumber. 4| 
Extensive correspondence with mill managers in various parts 
of the northern Rocky Mountains and Pacific coast range has elicted 
the fact that no accurate record is kept of the extent of the prevalence 
1 Sesia novaroensis Hy. Edw.; order Lepidoptera, family Sesiide. Identification by Mr. 
August Busck. 
2 The insect from the southern Rocky Mountains, after the rearing of three specimens, 
proves to be Sesia novaroensis. 
Norre.—This bulletin is of interest to entomologists as a contribution to their specialty, 
and to owners and manufacturers as a business proposition. 
93335 °—Bull. 255—15 1 
